Mobile bases for use with and forming part of robots and the like allow such devices to operate along relatively planar surfaces, such as a floor of an industrial facility. Such mobile robots are commonly used in industrial applications for transporting products from one location to another as well as aiding in the retooling of machines, including grinding and milling machines and fixed robots, the latter commonly referred to as pick-and-place robots.
Indeed, in most modern factory installations, there is a need for an integration of mobile robots with pick-and-place robots in order to achieve a high degree of productivity. Such mobile robots may be highly intelligent devices incorporating central computers to allow the devices to perform such decisional tasks as avoidance of obstacles, the manipulation of objects with respect to loading and unloading areas, and radio communication control with central computers so as to receive and execute tasks as designated to them from the central computer. It is important that the mobile robot, sometimes referred to as X-Y conveyors (a name which has been given to them by the Sumitomo Machinery Corp. of America of Teterboro, N.J.), be capable of maneuvering in relatively close quarters over surface irregularities and changes in the slope of a floor as may be encountered by ramps used in factories. It is also important that such mobile bases be capable of moving on slick surfaces such as caused by oil spillages and grease.
Thus, the mobile base for use with robots must be a versatile device capable of movement in any planar direction and also able to maneuver in and around obstacles and surface irregularities without falling over. This latter problem is complicated by the fact that objects lifted by a mobile robot tend to change the center of gravity of the robot and effectively make the mobile robot less stable than it otherwise would be. It is therefore necessary that the mobile base or carriage system used for a mobile robot be capable of adapting itself to such changes in the center of gravity of the robot-load combination and thereby effectively and safely transport an object from one location to another.
Some of the factors that have been considered in the design of present mobile bases include: (1) the overall efficiency of the mobile base in terms of the length of time that it can operate before it requires recharging or refueling; (2) the ability of the mobile base to negotiate surface discontinuities; (3) the maximum grade that can be safely ascended or descended by a mobile robot when the mobile robot is either a load or no-load condition; (4) the ability of a mobile robot to operate when the floor surface is coated with grease, oil, mud, snow, or other slide-inducing material; (5) the ability of a mobile robot to operate on surfaces which are not "hard"; such as carpets, lawns, linoleum, and the like, as well as considerations as to whether the mobile base will damage or mar such surfaces; (6) the maximum load that the mobile robot is designed to carry; (7) the minimum passage width (such as a door) through which the mobile base must be able to pass; (8) the maximum speed and acceleration required by the mobile base; (9) whether the mobile base must operate without exhaust and whether noise limits are present; and (10) the temperature and humidity range in which the mobile robot is to operate; (11) the maximum vibration the mobile robot is to encounter; (12) other environmental factors which may affect the operation of the mobile robot; and (13) the cost and reliability of the mobile base.
The prior art has approached the implementation of mobile bases from several design philosophies, one of which is the tricycle carriage system shown in FIGS. 2A and 2B. In FIGS. 2A and 2B, the carriage system uses two independent drive motors to respectively power and steer the robot. The driven wheels are fixed parallel to each other, while the third wheel is free to pivot. Steering is accomplished by causing one of the driven wheels to rotate faster than the other. This allows relatively tight turns to be accomplished by powering one wheel in a forward direction and the other in a reverse direction.
A primary problem with this configuration is that steering can be erratic due to differences in traction and/or efficiency between the two driven wheels. This can be partially corrected by placing an angular position encoder on the pivot wheel to help sense the rate of turning. If a pivot encoder is used, care is generally required during reverse movement or differential pivots. Alternatively, a computer can be used to provide tight control of the speed to the drive motors. This can be accomplished through use of tachometers to each drive motor or by using synchronous motors such as brushless rare earth motors and/or stepping motors. Representative of such carriage systems are those manufactured by R. B. Robotics Corporation, of 14618 West 6th Ave., Suite 201, Golden, Colorado 80401.
Another variation of the tricycle carriage system powers only the pivot wheel while the other two wheels freely rotate. In this variation, steering is accomplished by a gear motor coupled to control the direction of the powered pivot wheel. This alternative is generally less expensive than the first mentioned dual-driven wheel variation and allows simpler steering control. The traction of this latter system, however, is less than that for the dual-driven version.
As will be discussed further in this description, carriage systems are required to be highly stable if they are to operate safely in an industrial environment. In particular, it is important that they not only be able to maneuver along a factory floor or the like but also that they be able to do so without tilting or falling over due to changes in direction, speed or floor tilting. Important considerations must therefore be made with respect to determination of the center of gravity, both in the unloaded and loaded configurations of the overall mobile robot. This in turn involves calculation of dynamic turning forces to ensure that not only is the mobile robot stable when loaded, but that it will remain stable even when acceleration forces associated with turning or changing of speed are encountered separately or simultaneously with respect to each other.
Another prior art carriage system that uses a triangle principle has been developed by the U.S. Veterans Administration as a transport device for paraplegic people, called the Omnichair.TM.. This carriage system is described in a publication entitled "Microcomputer Controlled Omni-Directional Mechanism for Wheelchairs" by W. H. T. La, T. A. Koogle, D. L. Jaffee, and L. J. Leifer, from the Institute of Electronic Engineers publication Frontiers of Engineering in Health Care, CH1621-2/81/0000-0326,1981, IEEE. This technique uses what is known as a "wheel within a wheel" with rollers positioned about the periphery of each of the three main wheels. One such main wheel is shown in FIG. 3A and three such wheels are shown in FIG. 3B as attached to the chair base. The chair can be turned by driving all three wheels together, and can be translated by driving two of the three wheels. This latter situation is shown via force vectors in FIG. 3C.
The present invention approaches a carriage system design from a different perspective; namely, a technique which uses a plurality of wheels, each oriented in the same direction at the same time and each allowed to change its direction under the unified control of a steering mechanism. Drive to each wheel is also simultaneously directed to the wheels by means of a separate drive train. In this way, only one drive motor and one steering motor are used in order to achieve a mobile carriage system operable in any direction.
An enhanced version of this carriage system further includes an extensible leg assembly for each wheel with the respective wheel mounted at the end of the leg assembly. The leg assemblies are unifiedly controlled by a single motor driving a chain which operates the rotation of each of the extensible legs. The steering chain simultaneously adjusts each of the wheels so that as the legs extend or retract, the wheel orientations are maintained, when the mobile base is in translation and thus movement in any direction can be maintained without compensating for the retraction or extension of the leg assemblies. This greatly simplifies the use of the carriage system as it approaches or leaves a narrow passageway such as associated with doorways and the like.
Furthermore, through use of single motors for each of the steering, driving and leg control functions, a higher degree of efficiency is attained than in other prior art devices. This efficiency is markedly better than prior art carriage systems which turn the entire base in order to make a turn. Here, only the wheels and turret associated with the base turn while the remainder of the carriage system does not turn, thereby greatly reducing the energy required to make turns. This energy saving is especially important in warehouse and other applications requiring turns to be made frequently.
In addition to the prior art noted above, a number of prior art patents are known which are relevant to the present invention. These references are presented in Table 1 below.
TABLE 1 ______________________________________ Inventor Issue Date ______________________________________ U.S. Pat. No. 3,642,088 Smith 1972 3,825,087 Wilson 1974 3,938,608 Folco-Zambelli 1976 3,972,379 Norris 1976 4,274,503 Mackintosh 1981 Foreign References West Germany 2735071 Thale 1979 The Netherlands 6609100 Klockner-Werke AG 1967 ______________________________________
Of these references, U S. Pat. No. 4,274,503, Mackintosh is of greatest interest since it discloses a power operated wheelchair having a drive motor 87 and a steering motor 43 as shown in FIG. 2 thereof. The steering motor drives a steering chain 77 which in turn controls the direction of six ground wheels 64 as best seen in FIGS. 3 and 7. The actual steering of each wheel is accomplished through direct turning of yoke 74 via shaft 73 and sprocket 76. This arrangement provides for changing the angular direction of each of the wheels simultaneously but does not provide for allowing the wheels to move about a short radius as a turn is effected at a stationary location as is done in the present invention. The present invention provides for actual rotation about each wheel's axle as a turn is generated so that the wheel does not shimmy along the surface upon which it is placed. The arrangement shown in Mackintosh does not provide for such rotation, and thus shimmying about the surface upon which the chair is placed apparently will occur if a turn is effected while the chair is not in translation. Such shimmying requires a great deal of energy, thus reducing battery recharging times and can result in marring of the floor surface as well as rapid wearing of the ground wheels 64.
Furthermore, the embodiment shown by Mackintock includes six peripherally placed ground wheels which limit the amount of purchase, that is surface area upon which the steering chain contacts the sprockets 76 associated with the ground wheels. By having limited purchase, there is the likelihood of slippage between the steering chain and the sprockets, especially if a turn is attempted without translation of the chair which would result in high frictional forces between the ground wheel and the surface of the floor. The present invention typically employs three or four ground wheels and provides for rotation of these wheels about their axes when turns are performed; thereby minimizing frictional contact with the floor and reducing energy usage. The use of three or four wheels instead of six also greatly increases the purchase between the steering chain and the steering sprockets, and this in turn is also increased through the use of idlers about which the steering chain passes which increases the purchase beyond that associated with placement of the steering wheel about the outer periphery of each of the steering sprockets as done in Mackintosh.
Furthermore, the enhanced embodiment of the present invention has extensible leg assemblies that provide greatly increased stability of the mobile base when the legs are in their extended position. Mackintosh does not disclose or suggest such extensible leg assemblies.
U.S. Pat. No. 3,972,379, Norris, discloses a hydrostatically driven utility vehicle where each wheel is separately driven and steered and where means are provided for steering any two wheels in unison. The steering is accomplished with rack and pinion gear assemblies, unlike the present invention, and no suggestion of extensible leg assemblies is made in this reference.
U.S. Pat. No. 3,938,608, Folco-Zambelli discloses a wheeled vehicle having a guide and traction wheel 8 which turns as the body of the unit is turned with reference to its frame. This type of drive and steering mechanism is unlike the present invention and also does not suggest the extensible leg assemblies disclosed in the present invention.
U.S. Pat. No. 3,825,087, Wilson discloses a motorized agricultural type carrier in which all four wheels of the carrier can be selectively powered and steered. The steering mechanism shown is unlike the present invention. This reference also does not disclose or suggest extensible leg assemblies.
U.S. Pat. No. 3,642,088, Smith discloses a self-locating vertically and facing adjustable seat for use in tractors. Although the tractor has driven and steering wheels, this patent is of lesser relevance than the above cited references and does not disclose extensible leg assemblies nor the particular technique used to drive and steer the wheels of the mobile base disclosed herein.
German Pat. No. 27 35 071, Thale shows in its drawings a mechanism for steering pairs of legs in the same direction at the same time with two pairs of legs being steered oppositely so as to allow the device to move in a smooth circle as shown in its FIG. 1. This technique for steering the wheels of the device is unlike the present invention although FIG. 3 does show a gear assembly for driving a single wheel which is similar in nature to the present invention. This reference also does not disclose extensible leg assemblies.
Finally, Netherlands Pat. No. 6609100 shows a tricycle type power vehicle with apparent steering of the front wheel 8. This type of vehicle does not disclose or suggest the carriage system of the present invention with uniformly driven and steered legs and extensible leg assemblies.
Therefore, it is submitted that the prior art references. taken alone or in combination with each other, do not disclose or suggest the mobile base of the present invention, including the embodiment using extensible leg assemblies. Copies of the patent references cited will be submitted to the Patent and Trademark Office.